This invention relates to the transmission of digitally formatted data via a communication system employing a carrier modulated with phase shift keying (PSK) and, more particularly, to removal of phase ambiguities introduced in the analog signal transmission of the communication system for the case of modulation of the digitally formatted data by trellis coded modulation with Viterbi decoders.
A typical communication system includes a transmitter having an oscillator for generation of a carrier, and a receiver having an oscillator employed in reception of the carrier. A modulator within the transmitter is operative to modulate the carrier with a modulation such as phase shift keying, and a demodulator in the receiver is operative to demodulate the modulated carrier to extract data transmitted via the communication system. Such a communication system may be subject to phase ambiguities with consequent errors in the signal transmission, due to the presence of noise at the transmission end and/or the reception end of the communication system. Resolution of phase ambiguity in trellis coded modulated data is disclosed in U.S. Pat. Nos. 5,428,631 of Zehavi and 5,233,630 of Wolf which employ various types of encoding and decoding to resolve the phase ambiguity. Each of these patents also disclose components of a communication system with coding and decoding of Mary PSK modulated signals.
With the wide use of such communication systems in radio-telephony and in other areas which can benefit from a minimization of size and complexity of the electronic equipment, it is desirable to reduce the complexity of the circuitry. A problem arises in that the coding and decoding circuitry of the foregoing communication system is greater than that which is desired.